1. Technical Field
The present invention is related to a scanner motor.
2. Description of the Related Art
In an optical scanning device typically employed in, for example, a laser beam printer, the most important part is the scanner motor that rotates a polygonal mirror, which is provided for total reflection of a laser beam toward a photosensitive drum, at a high speed. Illustrated in FIG. 1 is a conventional scanner motor, which has a similar configuration to a small spindle motor employed in a small precision device.
Specifically, a shaft 1 is inserted in the center of a sleeve (not shown) to rotate, and a housing 4 is fitted on an upper end part of the shaft 1. Then, a polygonal mirror 3 is mounted firmly on an upper part of the housing 4. In order to fix the polygonal mirror 3, a compression spring 2 compresses the upper surface of the polygonal mirror 3.
In this state, if a rotational force is generated through an electromagnetic interaction between a magnet 5 and a coil 6, the generated rotational force is transferred to the housing 4 and the polygonal mirror 3 through the shaft 1 to rotate the polygonal mirror 3. Then, a laser beam is beamed to and reflected by the rotating polygonal mirror 3.
Meanwhile, the most important factor in a scanner motor is that the polygonal mirror 3 coupled to the housing 4 operate stably when the shaft 1 rotates. Specifically, even a small displacement of the polygonal mirror 3 may distort the reflection angle of the laser beam when the polygonal mirror 3 operates, deteriorating the printing property.
In the conventional technology, as illustrated in FIG. 1, a reflection surface 3a of the polygonal mirror 3 is close to a compression force acting point P of the compression spring 2, and thus the compression force of the compression spring 2 can also be applied to the reflection surface 3a of the polygonal mirror 3, distorting the reflection surface 3a. If the reflection surface 3a is distorted, a laser beam scanned to the polygonal mirror 3 may be reflected in an unpredictable direction, causing the deterioration of the printing property.